The chemistry of lead actors Bradley Cooper and Jennifer Lawrence is palpable, and O'Russell is quick to give them credit for the film's anticipated box office and awards success. The movie, about a young man and woman fighting their own battles with mental illness, is a genre-less film; comedy and drama intermingle seamlessly, and you're just as likely to cry as you are to laugh in the film's final scenes.

Moviefone caught up with O'Russell at the Toronto Film Festival, where he filled us in on his casting choices and how he approached the sensitive issue of mental illness.